I have a flake.nix for my software project and nix develop starts a development shell as you would expect.
What isn’t clear to me is how I express additional dependencies that I would like to be present in the shell but that are not required to build the software.
For example, I would like the kind Kubernetes cluster to be present in the shell so that I can start a local development cluster and deploy the software. This dependency is not needed to build the software.
One solution is to write a function with a parameter controlling the list of dependencies and then to define both packages and devshells as applications of this function.
Here’s an example from one of my recent projects of such a function application:
What isn’t clear to me is how I express additional dependencies that I would like to be present in the shell but that are not required to build the software.
As sandro said, nix shell nixpkgs#kind would just add kind to your PATH, but this is imperative.
Another declarative option would be to merge the two:
Many thanks. With your help I’ve figured this out. Since it may help somebody in the future here is a modification of the go-hello flake template that will start a local kind based Kubernetes cluster and deploy your code to it when nix develop is invoked. It deals with macOS and Linux cross-compilation too. Exiting the nix develop shell will destroy the kind cluster. The hooks deal with setting up your kubectl to talk to the cluster inside the shell.
{
description = "A simple Go package";
# Nixpkgs / NixOS version to use.
inputs.nixpkgs.url = "nixpkgs/nixos-22.05";
outputs = { self, nixpkgs }:
let
# to work with older version of flakes
lastModifiedDate = self.lastModifiedDate or self.lastModified or "19700101";
# Generate a user-friendly version number.
version = builtins.substring 0 8 lastModifiedDate;
# System types to support.
supportedSystems = [ "x86_64-linux" "x86_64-darwin" "aarch64-linux" "aarch64-darwin" ];
# Helper function to generate an attrset '{ x86_64-linux = f "x86_64-linux"; ... }'.
forAllSystems = nixpkgs.lib.genAttrs supportedSystems;
# Nixpkgs instantiated for supported system types.
nixpkgsFor = forAllSystems (system: import nixpkgs { inherit system; });
in
{
devShell = forAllSystems (system:
let
pkgs = nixpkgsFor.${system};
in
pkgs.mkShell {
nativeBuildInputs = [
pkgs.envsubst
pkgs.gzip
pkgs.kind
pkgs.kubectl
pkgs.mktemp
];
inputsFrom = [
self.packages.${system}.container
self.packages.${system}.go-hello-native
];
shellHook = ''
if [[ "$(kind get clusters -q | grep go-hello | wc -l)" -eq 0 ]]
then
kind create cluster --name go-hello
fi
t=$(mktemp)
cp ${self.packages.${system}.container} $t.gz
gzip -f -d $t.gz
kind load image-archive $t --name go-hello
rm -f $t
kubectl config use-context kind-go-hello
export tag=${self.packages.${system}.container.imageTag}
envsubst < deployment.yaml | kubectl apply -f -
trap "kind delete cluster --name go-hello" EXIT
'';
}
);
# Provide some binary packages for selected system types.
packages = forAllSystems (system:
let
pkgs = nixpkgsFor.${system};
# Cross-compilation on macOS produces output at a different path.
entrypointPath = if pkgs.system == "x86_64-darwin" || pkgs.system == "aarch64-darwin"
then "/bin/linux_amd64/go-hello"
else "/bin/go-hello";
in
rec {
go-hello-native = pkgs.buildGo118Module {
pname = "go-hello";
inherit version;
# In 'nix develop', we don't need a copy of the source tree
# in the Nix store.
src = ./.;
# This hash locks the dependencies of this package. It is
# necessary because of how Go requires network access to resolve
# VCS. See https://www.tweag.io/blog/2021-03-04-gomod2nix/ for
# details. Normally one can build with a fake sha256 and rely on native Go
# mechanisms to tell you what the hash should be or determine what
# it should be "out-of-band" with other tooling (eg. gomod2nix).
# To begin with it is recommended to set this, but one must
# remeber to bump this hash when your dependencies change.
#vendorSha256 = pkgs.lib.fakeSha256;
vendorSha256 = "sha256-pQpattmS9VmO3ZIQUFn66az8GSmB4IvYhTTCFn6SUmo=";
};
go-hello-linux = go-hello-native.overrideAttrs (final: prev: {
GOOS = "linux";
});
container = pkgs.dockerTools.buildImage {
name = "go-hello";
config = {
Entrypoint = [ "${go-hello-linux}${entrypointPath}" ] ;
};
};
});
# The default package for 'nix build'. This makes sense if the
# flake provides only one package or there is a clear "main"
# package.
defaultPackage = forAllSystems (system: self.packages.${system}.go-hello-native);
};
}